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    SubjectRe: [PATCH] WARN_ONCE(): use bool for boolean flag
    Daniel Walker escreveu:
    > On Sun, 2009-09-27 at 12:56 -0300, Cesar Eduardo Barros wrote:
    >> Daniel Walker escreveu:
    >>> On Sun, 2009-09-27 at 10:53 -0300, Cesar Eduardo Barros wrote:
    >>>> #define
    >>>> WARN_ON_ONCE(condition) ({ \
    >>>> - static int __warned; \
    >>>> + static bool __warned; \
    >>>> int __ret_warn_once = !!(condition); \
    >>> Could __ret_warn_once be bool also ? It looks like just another
    >>> conditional variable..
    >> Yes, it could (as long as either it is converted back to int in the
    >> return of the macro, or all users do not care about the macro's return
    >> type). However, the justification used for the printk_once patch (and
    >> this WARN_ONCE patch) does not apply directly anymore, since the code is
    >> different (to start with, it is not a static variable).
    > I did a couple kernel builds to test this on a small normal config,
    > vmlinux.base-line
    > text data bss dec hex filename
    > 6718958 497200 1082460 8298618 7ea07a vmlinux.base-line
    > <-- Your patch
    > text data bss dec hex filename
    > 6718590 497232 1082292 8298114 7e9e82

    I am still trying to understand why data increases (but not enough to
    offset the gains on text and bss). My own testing had the same
    qualitative result (x86-64 defconfig):

    text data bss dec hex filename
    8101271 1207116 992764 10301151 9d2edf vmlinux.warn.before
    8100553 1207148 991988 10299689 9d2929 vmlinux.warn.after

    > vmlinux.all-bool-converted
    > text data bss dec hex filename
    > 6718506 497232 1082292 8298030 7e9e2e vmlinux.all-converted
    > your changes drops the size 368 bytes, and if you convert the other
    > conditionals it drops it by another 84 bytes. Not much more, but it's
    > something.
    > So I think Rolands original reasoning still holds.. As far as people
    > needing an int output from WARN_ON() , I'm not sure that's happening
    > anyplace .. I can't imagine a sane usage for that..

    I took a quick look, and all uses seem to be directly in a boolean
    context (within an if()), so there would be no problem. Besides, the
    unlikely() all these macros end with does a double negation, meaning
    even if it is an int, it will be either 0 or 1 (but I am not sure I am
    reading these macros right - it seems CONFIG_TRACE_BRANCH_PROFILING
    turns all unlikely() into likely()).

    In fact, I was expecting no change at all, since gcc should be able to
    see it is being treated as a boolean (perhaps I am trusting gcc too
    much). And to make matters even more confusing, my own test changing all
    __ret_warn_once to bool and dropping the !! caused an _increase_ of 598
    bytes (x86-64 defconfig).

    text data bss dec hex filename
    8100553 1207148 991988 10299689 9d2929 vmlinux.warnret.before
    8101119 1207180 991988 10300287 9d2b7f vmlinux.warnret.after

    (And yes, data increased again.)

    Cesar Eduardo Barros

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